At present, multiple generator and prime mover (e.g., aircraft engine or auxiliary power unit (APU)) sizing methods typically require that the worst case electrical load power extraction requirements be satisfied by both the generators and the prime mover design. In the case of the generators, the total electrical load of the vehicle is summed up over all operational scenarios so as to represent the maximum rated capacity of the generators. For “More Electric” vehicle applications, which have been proposed to shift the primary power sources used for systems and services from pneumatic (engine bleed) and hydraulic sources to electric sources, this generator capacity can be so large that it poses a hardship for the prime mover to provide both the generator input horsepower as well as any other horsepower extraction (e.g., propulsion) tasks that it is required to perform over its operational envelope.
When sizing such prime movers, additional power output downsizing can be achieved in an effort to optimize program objectives (such as weight reduction), but usually at the expense of derating the output of the prime mover to various services under certain operational conditions (e.g., periods of multitasking, high temperature, low ambient air pressure). As a result, some or all of the prime movers typically must be increased in power extraction capacity or otherwise oversized to carry the load of the generators along with other accessories and provide the necessary propulsion. As a result, either or both of the prime movers and the generators must be oversized to ensure that electrical capacity is maintained and that the prime movers operate properly through their mission profile. This oversizing of the prime movers and the electrical system equipment drives up cost and weight for the prime mover and the electrical system and may hence present impediments to the vehicle program goals.